Stator for rotating electric machine and manufacturing method thereof

Abstract

The invention relates to a stator for an electric machine comprising a stator yoke (14) having a circular surface (16) and a plurality of stator teeth standing on the circular surface (16), each of the stator teeth (18) having, on the one hand, a stack (20) of plates made of grain-oriented steel (32) having a first end (22) connected to the yoke (14) and an opposite second free end (24) and, on the other hand, an electrical wire winding (25), each of the plates (32) extending in a direction normal to the circular surface (16) while the grains are oriented parallel to the normal direction. Each of the plates (32) is cut into a T-shape forming two outlets (38, 40) in such a way that the second free end (24) has two opposed free wings (42, 44); and each of the plates (32) is treated so as to disorient the grains at their two outlets (38, 40).

Description

DESCRIPTION Title of the invention: Rotating electrical machine stator and production method

[0001] The present invention relates to a stator for a rotating electrical machine for an electric or hybrid motor vehicle and to a method for producing such a stator.

[0002] Known rotating electrical machines called "axial flux" comprise a rotor installed coaxially between two stators.

[0003] The rotor comprises a disc divided into identical angular sectors, and the disc has one or more housings in each of the angular sectors for receiving one or more permanent magnets.

[0004] As for the two stators, between which the disk rotates, they each comprise a stator yoke having a circular receiving surface extending along a plane and a plurality of stator teeth regularly arranged at equal distances from each other on the circular receiving surface so as to be able to coincide with the angular sectors of the rotor.

[0005] The stator teeth each comprise a stack of grain-oriented steel plates, having a first end connected to the yoke and a second free opposite end capable of coming opposite the rotor disc.

[0006] Each of the stator teeth includes a winding of electric wire around the stack to be able to induce a magnetic field through it.

[0007] Also, each of said plates extends in a direction normal to the circular receiving surface, while the grains are oriented substantially parallel to said normal direction.

[0008] Reference may be made to document WO 2020 / 078667, which describes the implementation of such a material in a rotating electrical machine.

[0009] Grain-oriented steels are advantageously used in applications related to rotating machines because they offer better magnetic conductivity, precisely in the direction of grain orientation.

[0010] On the other hand, these materials exhibit strong magnetic resistance, or reluctance, when the magnetic field extends in a direction transverse to the orientation of the grains.

[0011] Also, the free end of the stator tooth stacks are separated from the rotor permanent magnets by a functional air gap, since the rotor is driven in rotational motion relative to the stator. And the performance of rotating electrical machines is conditioned, in particular, by the reduction of this air gap.

[0012] Also, a problem which arises and which the present invention aims to solve is to provide a stator allowing the reduction of this air gap without interfering with the other elements which already make it possible to improve the performance of the machines.

[0013] In order to solve this problem, and according to a first object, a stator for a rotating electrical machine for a motor vehicle is proposed, comprising a stator yoke having a circular receiving surface and a plurality of stator teeth regularly arranged at a distance from each other on said circular surface, each of the stator teeth comprising, on the one hand, a stack of grain-oriented steel plates, having a first end connected to said yoke and a second free opposite end, and on the other hand, a winding of electric wire around said stack, each of said plates extending in a direction normal to said circular receiving surface, while the grains are oriented substantially parallel to said normal direction.Each of said plates is cut into a T-shape, forming two opposite beaks, so that said second free end of said stack of plates has two opposite free wings formed by the beaks of the plates of said stack; and each of said plates is treated so as to disorient the grains at their two opposite beaks.

[0014] Thus, a characteristic of the invention lies in the use of plates cut into T shapes to form each of the stacks and, in addition, in the local treatment of each of these plates at the level of each of the two opposite beaks in order to locally disorient the grains of the steel at the level of these beaks.

[0015] In fact, the beaks of the plates allow two opposite free wings of the stack to be formed when they are stacked, which free wings allow the winding of electric wire to be retained.

[0016] However, the magnetic field lines which extend substantially parallel to said normal direction at the heart of the stack, diverge at the free end of the stacks, and tend to cross the free wings in a direction oblique to the normal direction.

[0017] However, the grains are oriented in a direction substantially parallel to the normal direction, including in the plates at the level of the free wings in the absence of treatment, and as steel has poor magnetic conductivity when the magnetic field lines intersect the direction of the grains, the free wings of the stacks offer high reluctance and high iron losses if the orientation of the grains is not modified at this level.

[0018] And precisely, according to the invention, the grains are disoriented at the level of the beak of the plates to reduce this reluctance.

[0019] Preferably, said grains are disoriented independently of each other in random directions. In this way, the steel locally becomes “unoriented grains”, so that the reluctance is lowered compared to the situation where the grains are oriented substantially parallel to said normal direction.

[0020] According to a non-limiting embodiment, the two opposite beaks of each of said plates are heat-treated to disorient said grains. By supplying thermal energy to the plates at the beaks, a metallurgical modification is caused which randomly redistributes the orientation of the grains.

[0021] Moreover, this local energy supply, after cutting the plates, is easy to implement.

[0022] According to another embodiment of the invention, the two opposite beaks of each of said plates are folded, or folded and unfolded along lines transverse to said beaks spaced from each other, to disorient said grains. This mechanical operation of bending and unbending the plates at the beaks, along transverse lines, also makes it possible to redistribute the orientation of the grains. This bending may consist of folding the beak portions against each other, for example at less than 90° and then unfolding them in reverse. Ultimately, the beak extends freely in the mid-plane of the steel plate.

[0023] Advantageously, the transverse bending lines of the beaks are substantially parallel to each other.

[0024] According to a hybrid embodiment of the invention, both heat treatment and mechanical treatment are carried out.

[0025] According to yet another variant, the two opposite beaks of each of said plates are engraved by a laser beam along longitudinal lines oriented towards the tip of said beaks and spaced apart from each other to disorient said grains. Such a technique makes it easy to modify the metallurgical structure of the steel without contact. In addition, it is easy to integrate into the usual production system for producing plates and stacks.

[0026] It also allows for a more random redistribution of grain orientation in the material.

[0027] Also, said longitudinal lines are preferably substantially parallel to each other. In this way, a random redistribution can be obtained locally.

[0028] According to a particularly advantageous, but in no way limiting, embodiment of the invention, said stator yoke is made of grain-oriented steel; and, said first end of said stack and the yoke portion located in the vicinity of said first end are treated so as to disorient the grains. The stator yoke may also be made of a superposition of grain-oriented steel plates. And, at the junction between the stack and said superposition of plates, the grains of the steel of the superposition extend substantially perpendicular to those of the steel of the plates of the stack. Therefore, the magnetic field lines generated by the winding of electric wire around the stack, which extend parallel to the direction of the normal, then extend perpendicular to the oriented grains of the plates of the superposition forming the yoke.As a result, locally, the cylinder head offers significant reluctance at the level of said junction.

[0029] Also, to remedy this, the first end of the stack and the portion of the yoke to which it is connected are, for example, treated using a laser beam as will be explained in more detail below so as to redistribute the orientation of the grains randomly at the junction.

[0030] In this way, the reluctance at the junction is reduced in the same way.

[0031] According to a particularly advantageous, but in no way limiting, embodiment of the invention, said stator yoke has a circular receiving surface of generally cylindrical shape. In other words, the electric machine The resulting rotating coil is called "radial flux". More precisely, the rotor rotates inside the stator and the magnetic field induced across the plate stacks extends in a radial direction.

[0032] According to another embodiment of the invention, said stator yoke has a circular receiving surface extending along a plane. In other words, the resulting rotating electrical machine is called “axial flux”.

[0033] According to another object, there is provided a method for producing a stator for a rotating electrical machine for a motor vehicle as described above, according to which a stator yoke is provided having a circular receiving surface and a plurality of stator teeth regularly set at a distance from each other on said circular surface, each of the stator teeth comprising, on the one hand, a stack of grain-oriented steel plates, having a first end connected to said yoke and a second free opposite end, and on the other hand, a winding of electric wire around said stack, each of said plates extending in a direction normal to said circular receiving surface, while the grains are oriented substantially parallel to said normal direction;and, each of said plates is cut into a T, forming two opposite beaks, each of said plates is treated so as to disorient the grains at the level of their two opposite beaks, so that said second free end of said stack of plates has two opposite free wings formed by the beaks of the plates of said stack.;

[0034] Preferably, said grains are disoriented independently of each other in random directions.

[0035] Other features and advantages of the invention will emerge from reading the description given below of particular embodiments of the invention, given for informational but non-limiting purposes, with reference to the appended drawings in which: [Fig. 1] is a partial schematic view in radial section of a stator according to the invention according to one embodiment; [Fig. 2A] is a schematic perspective detail view of [Fig. 1]; [Fig. 2B] is a schematic front view of an element of the object of [Fig. 2A]; [Fig. 3] is a schematic axial sectional view of an element illustrated in [Fig. 1] according to an alternative embodiment; [Fig. 4] is a schematic axial sectional view of an element illustrated in [Fig. 1] according to another variant embodiment; [Fig. 5] is a schematic side view of a stator according to the invention according to another embodiment; [Fig. 6] is a schematic front view of the detail along arrow F of the stator illustrated in [Fig. 5]; and, [Fig. 7] is a schematic perspective view from below of an element shown in [Fig. 6] along arrow Z.

[0036] [Fig. 1] partially shows a stator 10 inside which a rotor 12 is installed so as to be able to form a rotating electrical machine. The latter is called “radial flux”.

[0037] Thus, the stator 10 comprises a stator yoke 14 having a cylindrical internal surface with a circular base 16 and a plurality of stator teeth 18 regularly set at a distance from each other on the cylindrical surface 16.

[0038] Also, each of the stator teeth 18 comprises a stack 20 of grain-oriented steel plates which will be described below, which stack 20 extends radially between a first anchoring end 22, anchored in the stator yoke 14 and a second free opposite end 24 extending opposite the rotor 12. In other words, each of said plates extends in a direction normal to said circular receiving surface.

[0039] In addition, each of the stator teeth 18 comprises a winding 25 of electric wire so as to be able to induce a magnetic field through the stack 20 and extending in a radial direction R.

[0040] The rotor 12 has a cylindrical external surface with a circular base 26, which is provided with a plurality of permanent magnets 28 adjusted at a distance from each other and regularly spaced.

[0041] And the space which extends between the permanent magnets 28 and the second free ends 24 of the stack 20 of the teeth 18, constitutes the air gap 30.

[0042] Reference will now be made to [Fig. 2A], [Fig. 2B], [Fig. 3] and [Fig. 4] to describe in detail the stack 20 of grain-oriented steel plates.

[0043] Thus, the stack 20 is made from steel plates 32, cut into Ts from steel strips, called “electrical steel” of less than 2 mm generally. These 32 steel plates are for example cut by punching or stamping to be obtained at an advantageous cost.

[0044] This type of flat metallurgical product is specially designed to obtain particular magnetic properties and in particular, high magnetic permeability.

[0045] To do this, through metallurgical transformations, it is known to ensure that the grains of the steel are oriented in the same direction, precisely to obtain these particular properties.

[0046] Thus, the T-shaped steel plate 32 illustrated in [Fig. 2B], has a stem 35, and opposite each other, a foot 34 and a head 36. And it is cut so that the crystalline structures, or grains, are aligned parallel to each other, in a given direction D, from the foot 34 towards the head 36.

[0047] Also, the steel plate 32, due to its T-shaped structure, has two opposite beaks 38, 40, which extend laterally and end respectively in two points 39, 41. Consequently, the grains are oriented in the direction D, including at the level of the beaks 38, 40, and they thus extend there in a transverse direction relative to the beaks at 38, 40.

[0048] An object of the invention is to disorient the crystalline structures of the nozzles 38, 40 as will be explained below.

[0049] Steel plates 32 of the type illustrated in [Fig. 2B] are thus stacked and secured against each other to form the stack 20 illustrated partially in profile in [Fig.2A]. The steel plates 32 are coated with a varnish to electrically insulate them from each other. This known lamination technique makes it possible to reduce eddy currents through the stack 20.

[0050] Thus, the beaks 38, 40 of the stacked steel plates 32 form two opposite free wings 42, 44.

[0051] In [Fig. 3] we find the stack 20 anchored in the yoke 14. In addition, we find the winding 25 of electric wire around the stack 20 between the yoke 14 and the two opposite free wings 42, 44.

[0052] Also, it will be observed that the cylinder head 14 is also made of stacked grain-oriented sheets. And the grains are oriented in a direction L perpendicular to the direction D in which the grains of the steel plates are themselves oriented.

[0053] Furthermore, when the electric wire of the winding 25 is powered, then it induces a magnetic field in the heart of the winding 20 oriented in the direction D of the oriented grains.

[0054] On the other hand, outside the winding 25, both at the first anchoring end 22 and at the second free opposite end 24, the magnetic field tends to diverge and the field lines, two of which 46, 48 have been partially shown for illustrative purposes, curve outwards and move away from each other. In other words, the magnetic field, in particular in the two opposite free wings 42, 44, becomes inclined relative to the orientation of the grains. As a result, the magnetic permeability decreases, and it is the object of the invention to overcome this.

[0055] To do this, and according to a first variant embodiment as illustrated in [Fig. 3], the two opposite beaks 38, 40 of each of the plates 32 are etched by means of a laser beam along first longitudinal etching lines 50, 52 oriented towards the tip 39, 41 of the beaks 38, 40. The first etching lines 50, 52 are spaced from each other and are preferably parallel to each other, in order to be able to disorient said grains in the beaks 38, 40 in a homogeneous manner.

[0056] For example, the first etching lines 50, 52 are respectively inclined at an angle of between 60° and 80° relative to the original direction D of the crystal structures.

[0057] This local treatment at the level of the beaks 38, 40 of the plates 32, does not allow the grains to be reoriented in another same direction, but to ensure that their orientation is distributed randomly. Consequently, and statistically, fewer grains, or crystalline structures, are oriented in an inclined manner relative to the magnetic field lines 46, 48.

[0058] Therefore, the magnetic permeability decreases less compared to a situation where the grains remain oriented in the same original direction D. This improves the performance of the rotating electrical machine.

[0059] This treatment operation using a laser can be carried out on each of the steel plates 32, and each of their beaks 38, 40, prior to their stacking.

[0060] Also, after the assembly of the steel plates 32, and that of the stack 20 thus formed on the yoke 14, the first end 22 of the stack 20 and the yoke portion in which the first end 22 is anchored, are also treated so as to disorient the grains.

[0061] To do this, second etching lines 54, 56 are made by means of a laser beam straddling the first end 22 of the stack 20 and the yoke 14. These second etching lines 54, 56 are respectively inclined substantially by 45° relative to the direction D of orientation of the grains of the plates 32 and to the direction L of the grains of the stacked sheets of the yoke.

[0062] In this way, the grains are locally disoriented at the junction between the stack 20 and the yoke 14, in a random manner to avoid lowering the magnetic conductivity when the magnetic field tilts relative to the orientation of the grains of the yoke 14 of the first end 22 of the stack 20.

[0063] The use of a laser beam is advantageous because it allows for local, remote processing without contact with the material. Furthermore, it is easily industrializable on existing production lines.

[0064] According to another embodiment, thermal energy is supplied to the tips 38, 40 of the steel plates 32, by any means, in order to be able to disorient the crystalline structures and thus improve the magnetic conductivity.

[0065] According to yet another embodiment variant, illustrated in [Fig. 4], a mechanical action is exerted on the beaks 38', 40' of the steel plates 32'. The references given in [Fig. 4] are identical to those given in [Fig. 3] and they are assigned a prime sign: "'", making it possible to distinguish this embodiment variant from the previous one.

[0066] We thus find in [Fig. 4], partially the stack 20', and its two opposite free wings 42', 44' formed by the beaks 38', 40' of the steel plates 32'.

[0067] According to this third embodiment variant, the two opposite beaks 38', 40' of each of the plates 32' of the stack 20' are folded and unfolded respectively along transverse fold lines 58, 60 to the beaks 38', 40', spaced from each other to also disorient said grains.

[0068] For each beak 38', 40' the transverse folding lines 58, 60 respectively are parallel to each other. Also, the beaks 38', 40' of each of the steel plates are folded regularly from the base to the tip 39', 41'.

[0069] Advantageously, the transverse fold lines 58, 60 extend in a direction inclined relative to the direction D' of orientation of the crystalline structures of the steel plates, by an angle of between 20° and 45°. In this way, a random redistribution of the orientation of the crystalline structures in the beaks 38', 40' is obtained.

[0070] Additionally, in one variant, the nozzles are both heat treated and bent to achieve a better random distribution of grain orientation.

[0071] According to another embodiment of a rotating electrical machine, called “axial flux”, as illustrated schematically in [Fig. 5], the stator 10” comprises a stator yoke 14” having a first circular surface 16” extending along a plane P and a plurality of stator teeth 18” regularly set at a distance from each other on the circular surface 16”.

[0072] Also, each of the stator teeth 18” comprises a stack 20” of grain-oriented steel plates, substantially trapezoidal, and which will be described in more detail below, which stack 20” extends radially between a first anchoring end 22”, anchored in the stator yoke 14” and a second free opposite end 24” extending opposite the rotor 12”.

[0073] Each of the 18” stator teeth comprises a winding of electric wire not shown for reasons of clarity of the drawing, so as to be able to induce a magnetic field through the 20” stack and extending in an axial direction A.

[0074] The 12” rotor has a second circular surface 26”, which is provided with a plurality of 28” permanent magnets adjusted at a distance from each other and regularly spaced.

[0075] And the space extending between the 28” permanent magnets and the second free ends 24” of the 20” stack of 18” teeth, constitutes the 30” air gap.

[0076] [Fig. 6] shows the 10” stator and its 14” stator yoke on which four 18” trapezoidal stator teeth are installed for illustrative purposes only.

[0077] These 18” trapezoidal stator teeth are seen from their second free end 24”, and we can distinguish their two opposite free wings 42”, 44”, whose 38”, 40” beaks of the 32” steel plates which constitute them are treated to disorient their crystalline structures.

[0078] Also, it will be observed that the two opposing free wings 42”, 44” diverge from each other from the center, identified by the axial direction A, towards the outside. In other words, the width of the 32” steel plates forming the 20” stack gradually decreases from the center towards the outside, although the 32” plates have the same general shape.

[0079] Thus, we find in [Fig. 7] a single 20” stack of trapezoidal section. It is made of a succession of 32” grain-oriented steel plates between a first 62” narrow plate and a last 64” wide plate. On the other hand, the opposite 38”, 40” beaks of the intermediate plates between the first 62 and the last 64, extend laterally by the same amplitude and have the same shape so as to form the two opposite diverging free wings 42”, 44”.

[0080] Also, the opposing 38”, 40” beaks of all plates were heat treated to disorient the crystal structures, or grains; the crystal structures of the rest of the plates remained aligned from the first anchoring end 22” to the second free end 24”.

[0081] Therefore, just as in the first implementation mode, the magnetic conductivity of the two opposing diverging free wings 42”, 44” is improved thanks to a random reorientation of the crystalline structures, or grains.

[0082] In this way, the performance of the rotating electrical machine is improved.

[0083] The invention also relates to a method for producing a stator 10 of a rotating electrical machine for a motor vehicle.

[0084] According to said method, a stator yoke 14 is provided having a circular receiving surface 16 and a plurality of stator teeth 18 regularly spaced apart from each other on the circular surface 16.

[0085] In order to produce these stator teeth 18, grain-oriented steel plates 32 are provided, and each of the plates 32 is cut into a T shape, forming two opposite beaks 38, 40. Then, each of the plates 32 is treated so as to disorient the grains at their two opposite beaks 38, 40.

[0086] The treatment can be carried out according to the treatment methods mentioned above. Advantageously, the grains are disoriented independently of each other in random directions. In other words, the grains are no longer oriented in a preferred direction and their orientation is distributed randomly in the nozzles 38, 40.

[0087] A stack of steel plates is thus formed having a first end 22, opposite a second free end 24, then forming two opposite wings 42, 44 constituted by the beaks of the plates of the stack.

[0088] Also, for each of the teeth, an electric wire 25 is wound around the stack, each of the plates 32 then extends in a direction normal to the circular receiving surface 16, while the grains of the plates are oriented substantially parallel to said normal direction, except at the level of their two opposite beaks 38, 40.

Claims

CLAIM

1. A stator (10) for a rotating electric motor vehicle, comprising a stator yoke (14) having a circular receiving surface (16) and a plurality of stator teeth (18) regularly spaced apart on said circular surface (16), each stator tooth (18) having, on the one hand, a stack (20) of grain-oriented steel plates (32), having a first end (22) connected to said yoke (14) and a second free opposite end (24), and on the other hand, a winding of electric wire (25) around said stack, each of said plates (32) extending in a direction normal to said circular receiving surface (16), while the grains are oriented substantially parallel to said normal direction; characterized in that each of said plates (32) is cut into a T by forming two opposite beaks (38, 40), so that said second free end (24) of said stack (20) of plates has two opposite free wings (42, 44) formed by the beaks of the plates of said stack; and in that each of said plates (32) is treated so as to disorient the grains at the level of their two opposite beaks (38, 40).

2. Stator according to claim 1, characterized in that said grains are independently disoriented from one another in random directions.

3. Stator according to claim 1 or 2, characterized in that the two opposing nozzles (38, 40) of each of said plates (32) are heat-treated to disorient said grains.

4. Stator according to any one of claims 1 to 3, characterized in that the two opposing nozzles (38', 40') of each of said plates are bent, or bent and unbent along transverse lines (58, 60) to said nozzles spaced apart from each other to disorient said grains.

5. Stator according to claim 4, characterized in that said transverse lines (58, 60) are substantially parallel to each other.

6. Stator according to any one of claims 1 to 5, characterized in that the two opposing nozzles (38, 40) of each of said plates (32) are engraved by a laser beam along longitudinal lines (50, 52) oriented towards the tip (39, 41) of said beaks and spaced apart from each other to disorient said grains.

7. Stator according to claim 6, characterized in that said longitudinal lines (50, 52) are substantially parallel to each other.

8. Stator according to any one of claims 1 to 7, characterized in that said stator head (14) is made of grain-oriented steel, and in that said first end (22) of said stack and the portion of head located in the vicinity of said first end are treated so as to disorient the grains.

9. Stator according to any one of claims 1 to 8, characterized in that said stator head (14) has a circular receiving surface (16) of generally cylindrical shape.

10. Stator according to any one of claims 1 to 8, characterized in that said stator head (14”) has a circular receiving surface (16”) extending along a plane.

11. A method for producing a stator (10) for a rotating electric machine for a motor vehicle according to any one of claims 1 to 10, characterized in that a stator head (14) is provided having a circular receiving surface (16) and a plurality of stator teeth (18) regularly spaced apart on said circular surface (16), each of the stator teeth (18) comprising, on the one hand, a stack (20) of grain-oriented steel plates (32), having a first end (22) attached to said head (14) and a second free opposite end (24), and on the other hand, a winding of electric wire (25) around said stack, each of said plates (32) extending in a direction normal to said circular receiving surface (16), while the grains are oriented substantially parallel to said normal direction;and in that each of said plates (32) is cut into a T shape, forming two opposing beaks (38, 40), and each of said plates (32) is treated so as to disorient the grains at the level of their two opposing beaks (38, 40), so that said second free end (24) of said stack (20) of plates has two opposing free wings (42, 44) formed by the beaks of the plates of said stack.;

12. A production method according to claim 11, characterized in that said grains are disoriented independently of each other in random directions.

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